Antihypertensive medications currently used in the treatment of hypertensive urgencies are limited due to deleterious side effects or requirements for sophisticated monitoring techniques. Labetalol HCl (Trandate) is a unique adrenergic blocking agent that can smoothly lower blood pressure following bolus injection without increasing heart rate or cardiac output. This study evaluates the efficacy and safety of intravenous boluses of labetalol HCl in the treatment of patients presenting to the hospital with a diagnosis of hypertensive urgency (diastolic blood pressure greater than or equal to 110 mm Hg). After baseline blood pressure and heart rate were recorded, 20 consecutive patients were treated with an initial 20-mg bolus of labetalol. Additional boluses of 40, 80, and 160 mg were administered at least 10 minutes apart in a step-wise fashion until control of blood pressure (diastolic blood pressure less than 100 mm Hg) was achieved or a total of 300 mg had been given. Blood pressures and heart rates were recorded at the time of response or following the last dose of labetalol. Mean (+/- SEM) supine systolic blood pressure decreased from 185 +/- 3 to 155 +/- 4 mm Hg (P less than 0.05) following labetalol therapy, and mean supine diastolic pressure decreased from 120 +/- 2 to 98 +/- 2 mm Hg (P less than 0.05). Mean heart rate did not change significantly. Eighteen of the 20 patients exhibited a therapeutic response; nine patients received a total of 20 mg, six required 60 mg, two required 140 mg, one received 300 mg. Of the two patients who did not respond, one received the maximum dose (300 mg).(ABSTRACT TRUNCATED AT 250 WORDS)